The invention relates to dicyanatochalcones of the general formula 
in which R1 to R8 independently of one another are hydrogen, C1-4-alkyl, C1-4-alkoxy or halogen.
Here and below, C1-4-alkyl is to be understood as meaning all linear or branched primary, secondary and tertiary alkyl groups having 1 to 4 carbon atoms, i.e. methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl and tert-butyl.
Correspondingly, C1-4-alkoxy is to be understood as meaning the groups composed of C1-4-alkyl and oxygen.
Halogen is to be understood as meaning fluorine, chlorine, bromine and iodine, in particular chlorine and bromine.
Difunctional aromatic cyanates, such as, for example, 2,2-bis-(4-cyanatophenyl)propane, which is derived from bisphenol A, are starting materials for polytriazine resins which, due to their high heat resistance and favourable mechanical and electrical properties, are used more and more frequently. In spite of these advantages, their properties are not yet satisfactory in all respects. Thus, for example, flexibility, impact strength, elongation at break and tear strength are insufficient for certain applications, and the exothermic reaction during curing may furthermore lead to problems.
Accordingly, it was the object of the present invention to provide novel aromatic cyanates which liberate little heat during cyclotrimerization to give polytriazines and yield polytriazines having improved mechanical properties.
This object is achieved according to the invention by the dicyanatochalcones of the invention.
It has been found that dicyanatochalcones of the general formula 
in which R1 to R8 independently of one another are hydrogen, C1-4-alkyl, C1-4-alkoxy or halogen, give off only little heat during cyclotrimerization to give polytriazines. Furthermore, they yield polytriazine resins having high flexibility, impact strength, tear strength and elongation at break and a low permittivity. Moreover, in the event of fire, they give off only small amounts of low-toxicity flue gas. Furthermore, the peak heat release during combustion of the cured resins and/or components is extremely low compared to the cyanate esters or other resin systems which have been available to date.
Particular preference is given to 1,3-bis-(4-cyanatophenyl)-2-propen-1-one of the formula 
The dicyanatochalcones according to the invention can be prepared by reacting a dihydroxychalcone of the general formula 
in which R1 to R8 are as defined above with cyanogen chloride or cyanogen bromide and a tertiary amine.
The dihydroxychalcones (II) are known compounds, or they can be obtained from the corresponding substituted benzaldehydes and acetophenones, analogously to known processes.
The reaction of the dihydroxychalcone (II) is preferably carried out using cyanogen chloride.
A particularly preferred tertiary amine is triethylamine.
The examples below illustrate the preparation of the compounds according to the invention, without imposing any limitations.